Untreated, severe hyponatraemia may result in cerebral oedema, which in turn can cause brain herniation. It is therefore important to promptly identify and treat hyponatremia appropriately. However, the particular management for each patient is based on a number of factors listed below. Further to this, over-rapid correction may result in osmotic demyelination syndrome.

Principles

Management of hyponatremia is complicated and primarily based on the following parameters:

• duration of hyponatremia: is it acute or chronic?
  • acute: develops over a period of < 48 hours
  • chronic: develops over a period > 48 hours
• the severity of hyponatremia: what is the sodium level?
  • mild: 130-134 mmol/L
  • moderate: 120-129 mmol/L
  • severe: < 120 mmol/L
• symptoms: is the patient symptomatic?
  • patients with mild hyponatraemia may be symptomatic
  • early symptoms may include: headache, lethargy, nausea, vomiting, dizziness, confusion, and muscle cramps
  • late symptoms may include: seizures, coma, and respiratory arrest
• the suspected aetiology of the hyponatraemia:
  • hypovolemic hyponatraemia/clinically dehydrated: diuretic stage of renal failure, diuretics, Addisonian crisis
  • euvolemic hyponatraemia: SIADH
  • hypervolaemic hyponatraemia: heart failure, liver failure, nephrotic syndrome

Management

Initial steps in all patients

• exclude a spurious result (e.g. blood taken from a drip arm)
• review medications that may cause hyponatraemia

Chronic hyponatreamia without severe symptoms

If a hypovolemic cause is suspected

• normal, i.e. isotonic, saline (0.9% NaCl)
• this may sometimes be given as a trial
  • if the serum sodium rises this supports a diagnosis of hypovolemic hyponatraemia
  • if the serum sodium falls an alternative diagnosis such as SIADH is likely

If a euvolemic cause is suspected

• fluid restrict to 500-1000 mL/day
• consider medications:
  • demeclocycline
  • vaptans (see below)

If a hypervolemic cause is suspected

• fluid restrict to 500-1000 mL/day